1. Field of the Invention
The present invention relates to a method of and apparatus for cooling and cleaning the lower sealing valves of the storage hoppers of shaft furnace charging installations. More particularly, this invention is directed to cleaning and cooling the sealing valves of a bell-less blast furnace charging installation in which the sealing valves are directly subjected to the temperature prevailing at the furnace throat. This invention is thus generally directed to a novel and improved method and apparatus for sealing the storage hoppers or bins of a shaft furnace charging installation.
2. Description of the Prior Art
On modern high capacity blast furnaces, in place of the hitherto conventional furnace-top distributors comprising a charging hopper arranged on the furnace throat and sealed by means of upper and lower bell-type charge distributors, increasing use is being made of one or more charge material intermediate storage bins which are selectively isolated from the conditions prevailing within the furnace and the ambient atmosphere by sealing valves or flaps. These valves or flaps are removed from the flow of charge material during the furnace charging operation.
U.S. Pat. No. 3,693,812 discloses a bell-less shaft furnace charging installation including a distribution chute, which is rotatable and adjustable in pitch angle, positioned in the blase furnace throat. In the apparatus of U.S. Pat. No. 3,693,812 the charge material or burden is stored in two or more intermediate storage bins or hoppers and is supplied to the distribution chute in controlled quantities, through use of a metering device, via a central feed channel. In the manner known in the art, the storage bins are operated in accordance with a predetermined cycle, i.e., while one of the bins is being filled with charge material the other will be discharging its contents to the central feed channel and thence onto the furnace hearth via the distribution chute.
Prior to each charging operation and before the start of the refilling of a previously discharged storage bin with charge material from the material pit, the pressure in the storage bin to be discharged or filled must be equalized with the pressure existing in the blast furnace throat or with the ambient atmospheric pressure. This requisite pressure equalization is accomplished by supplying blast furnace gas at furnace pressure to the storage bin or releasing this gas to the atmosphere as appropriate. In the interest of sealing the storage bins relative to the blast furnace port or to the atmosphere, the bins are preferably provided with upper and lower sealing valves or flaps.
Due to the relatively large size and weight of the sealing valves, and also as a consequence of the high temperature and other harsh operating conditions encountered in the environment of a shaft furnace, metal-to-metal seals rapidly degrade and will not provide adequate sealing of the high pressures established inside of the furnace after a relatively short operational life. The rapid deterioration of metal-to-metal seals dictates the use of soft or resilient materials to achieve adequate sealing. To insure that the quality of the seal is maintained during operation for a reasonably long period of time, steps must be taken to insure that the sealing surfaces of the sealing flaps of a shaft furnace charging installation are not subjected to erosion induced wear by the charge material. Also, a sealing material which can withstand the heat and pressure stresses of the operating environment must be selected. The requirement that the sealing surfaces of the valves be protected against erosion induced wear is partially satisfied by insuring that the sealing flaps do not perform a material retaining function; separate flow control members located upstream of the lower sealing valves in the direction of material flow being employed for this purpose. Additionally, in the open condition, during the charging or burdening of the furnace the sealing valve flaps are rotated so as to be completely removed from the material flow path.
A sealing material which satisfactorily withstands, over a sufficiently long operational life, the heat and pressure stresses to which the lower sealing flaps of the storage bins are subjected is not presently available. A furnace charging operation necessarily produces great temperature differences in the region surrounding the lower sealing flaps. During the "dead" time between individual charging operations the blast furnace heat is lead, by convection of the throat gas, to the underside of the lower sealing flaps. The conductivity of the gas, and thus the temperatures to which the sealing flaps are exposed, is increased by the high counterpressure at the throat in modern blast furnaces. During the charging process, however, the temperature in the area of the opened lower sealing flaps falls abruptly as a result of the presence and flow of the charge material which is at the temperature of the ambient atmosphere surrounding the furnace. Due to the large temperature differences and the sudden changes in temperature, sealing materials mounted in or on the lower sealing valves of a blast furnace charging installation could be expected to be considerably stressed and deformed leading to early impairment of the sealing characteristics.
Moreover, the temperature in the blast furnace can vary from the normal operating temperature of 200.degree. to 250.degree.C to 500.degree.C or more. It is even possible that brief temperature surges of approximately 1000.degree.C may occur. As a result of these high temperature influences the sealing material of the lower sealing flap is stressed to its limits and consequently the life and sealing characteristics of the lower flap seal are considerably impaired.
In addition, after each charging operation the storage bins and their discharge channels are filled with very hard and sharp-edged dust particles. These particles cling to the sealing surfaces of the sealing valves, especially when the charging material has a high moisture content. If these particles are not removed they will begin to accumulate between the sealing surfaces on the valve or flap members and their cooperating stationary bearing or seating surfaces. With each closing operation of the sealing flap the sealing material becomes further incrusted with these deposits of dust particles whereby the sealing action is considerably reduced or destroyed after a relatively short period of time.